An operating method of the type mentioned at the beginning is known for example from US 2008/060403 A1. Said document explains a way in which the continuous operation of the continuous rolling train can be maintained despite the fact that the rolling stock passing through the continuous rolling train has a critical transition region which cannot be rolled safely. In essence, the teaching of US 2008/060403 A1 concerns tracking the path of the transition region through the continuous rolling train and lifting each of the roll stands of the continuous rolling train when the critical transition region reaches the respective roll stand and screwing down the respective roll stand on the rolling stock again and continuing the rolling process when the critical transition region has passed the respective roll stand. The rolling stock is thus rolled in the roll stands of the continuous rolling train only outside the critical transition region. The critical transition region itself and parts of the rolling stock adjoining the critical transition region pass through the entire continuous rolling train without being rolled.
In continuous rolling trains, rolling stock should be rolled with as little interruption as possible (that is, continuously). Therefore, at the entry side of the continuous rolling train, individual coils are brought together and connected to one another—generally by means of welding. This approach is taken in particular for the cold rolling of sheet metal, that is to say a strip-shaped rolling stock.
The rolling of the rolling stock causes the rolls of the roll stands to wear. Here, within one of the roll stands, the most intense wear occurs in the working rolls of the respective roll stand. Support rolls and—if present—intermediate rolls wear only to a lesser extent. In terms of the continuous rolling train as a whole, the wear increases toward the exit side of the continuous rolling train.
In the prior art, to exchange rolls of a roll stand, it is known to bring the continuous rolling train to a stop, wherein the rolling stock remains in the continuous rolling train, that is to say is merely brought to a halt. As a result of the stoppage, rolling defects are generated at the stoppage points of the rolling stock. The rolling defects may comprise in particular dimensional defects and surface defects. If relatively high demands are placed on the quality of the rolling stock, that part of the rolling stock in which the rolling defects occur must be scrapped. Here, that part of the rolling stock which is to be scrapped may have a considerable length, for example 50 to 100 m. Furthermore, operational efficiency is reduced on account of the temporary stoppage of the continuous rolling train.